After promising a "battle for control of petroleum," President Hugo Chavez implored Venezuela's oil industry today to return to work as the country appeared close to running out of gasoline on the seventh day of a national strike designed to force him to resign or hold new elections.

National Guard troops wearing combat helmets and carrying assault rifles were deployed to every gas station in the city, apparently to keep them open and protect against panic buying. Lines stretched 15 cars long, and some station owners predicted that supplies would be gone by day's end. Many stations in central and western Venezuela had closed on Saturday.

"We're sending in our orders [for more gasoline], but no one is taking care of them," said Adrian Bendeck, the general manager of 83 ChevronTexaco stations across the country. He spent the day at his flagship station in the Las Mercedes neighborhood, where seven soldiers watched over the 25 pumps and the lines of cars that spilled onto the main avenue. He said 10 percent of his stations had closed.

As fuel supplies dwindled, Venezuela's national strike, which has crippled the vital oil industry and hurt many small businesses during the peak retail season, showed no sign of lifting. Opposition leaders tonight called it "successful and growing" and extended it at least another day.

Angered by the president's leftist politics, strident class-based rhetoric and tilt toward Cuba, a politically diverse opposition is hoping the strike forces the twice-elected Chavez to resign or move up the 2006 elections.

The strike has intensified the political struggle that has gripped the country of 23 million people for much of the year, highlighted by a military-led coup in April that briefly removed Chavez from office. On Friday, a 37-year-old drifter, Joao De Gouveia, allegedly opened fire with a pistol on an opposition demonstration, killing three people and wounding 29 others. He was brought before a judge today -- six others are also being held -- as anti-government protesters gathered to bury 18-year-old Keyla Guerra, the youngest victim of the shooting.

At the same time, talks mediated by Cesar Gaviria, secretary general of the Organization of American States, appeared to have taken a positive turn after a week's suspension. A source involved in the talks said government and opposition negotiators have agreed to meet Monday to begin the first formal discussion of an electoral solution to the standoff, including a nonbinding referendum on Chavez's administration and the possibility of creating a citizen assembly to amend the constitution to allow early elections.

Gaviria, backed by the United States, favors elections as the best solution to Venezuela's crisis. "The door to negotiations is open," he said. "That's what was most important."

But it was clear today that Chavez, who delivered a withering attack on the opposition during his weekly call-in show, has made restoring his authority over the national oil industry his top priority. His deployment of troops to filling stations and the retaking of an oil tanker in Lake Maracaibo suggested he would use force, if necessary. He has promised a major restructuring of Petroleos de Venezuela, the national oil company that provides the government with $9 billion a year in revenue and the United States with 1.5 million barrels a day, or 15 percent of its oil imports.

Navy forces have occupied the tanker, Pilin Leon, but a replacement crew could not be found today to pilot the ship, carrying 280,000 barrels of gasoline, to port. The cargo represents a little more than Venezuela's daily gasoline consumption. More than a half-dozen other tankers remain at anchor in support of the strike.

"Assume your responsibility not only to the petroleum industry but to the country," said Chavez, addressing oil workers. "You are operating an industry that is the heart" of Venezuela.